1. Mobile to Account for More than Half of Digital Ad Spending in 2015https://www.emarketer.com/Article/Mobile-Account-More-than-Half-of-Digital-Ad-Spending-2015/1012930
2. UK Mobile Ad Spend ’To Overtake Print and TV’https://www.theguardian.com/media/2015/sep/30/mobile-advertising-spend-print-tv-emarketer
3. Pew Research Center: Search Engine Use 2012http://www.pewinternet.org/2012/03/09/search-engine-use-2012/